Keyframing emission shader colour/strength using python
You need to get a bit closer to what you want to keyframe. It is the socket that keyframes one of it's values, not the material. So you want to tell the input socket to insert a keyframe.

So this slight variation of what you have will work (only over two lines for clarity) -

node = bpy.context.active_object.active_material.node_tree.nodes['Emission']
node.inputs[1].keyframe_insert(data_path="default_value",frame=10)